Geochemical surveying



April 1 7, 1,945. E, E RQPER 2,374,135

I GEOCHEMICAL sURvEYING I Filed Feb. 13, 1941 zshets-sheet;

Patented Apr. l?, 1945 UNITED, STATES PATENT y or-Flcla K a. a e 2,314,135

GnocnEMIcAL sUavEYrNG Edwin E. nacer, Tulsa, om.. assigner to samo-` l llnll -Olland Gas Company, Tulsa, Okla., a corporation of Delaware Y Application February 13, 1941, serial No. 313,185

ciaims. (c1. 20a-zus) l"I'his application pertains to theart of `geochemical surveying. As this term is now used it refers to the detection of minuteamounts of hydrocarbons at or near the surface of the earth which have migrated upwards from subterranean accumulations of oilpr gas and which accordingly, by their relative abundance orrarity, serve as indicators of the presence of such subterranean accumulations.

` Numerous investigators have worked with varying success in the last few -years at the problem of determining the presence of subterranean petroleum accumulations by direct methods rather than by geophysical or geological investigation. The main hypothesis involved is .that these hydro'- carbon deposits have been under great pressure for a long period of time at a relatively elevated temperature and that they are vmade up of constituents some of which are relatively highly volatile. `It has been postulated, therefore, that lighter hydrocarbons from the deposit have through the time since the accumulation of the petroleum slowly migrated upward through the strata lying above the' pool, eventually to be dissipated into the atmosphere. Obviously; 'the quantities which have thus migrated are of an extremely minute amount due to the relatively low permeability of the earth,'among other factors. Thus at or near the surface of the. earth the soil atmosphere or soil air should contain a very small quantity of some o'f the lighter petrcliferous hydrocarbons. if there is an oil or gas pool below.' i' Since' thevsoil itself is .to a certain extent a sorbent, some of the hydrocarbons which have migrated to this point are sorbed on the surface of the ne grains of earth. 'Ihis quantity will be dependent uponl numerous factors including ythe partial pressures of the hydrocarbons inthe soil gas, .their molecular weights, the sorptive capacity of the soil, the temperature of the soil particles, etc.

Investigators have attempted to determine by Y various analytical procedures the presence or absence of hydrocarbons in the soil air or sorbed on the surface of` soil samples in order to .determine the presence of the-underground reservoirs. It v.was discovered that the presence of methane in the soil air or sorbed on the soil itself was of relatively negligible value as an indicator becauseA methane is not only a constituent of pelsiderable amounts wherever-there; is decaying -vegetable matter. Studies on the presence of the higher parailinic hydrocarbons, ethane, propane, etc., offered more theoretical advantage because such materials are apparently not; evolved ents present in the sample. l .i

The two main methods of gathering a sample have been mentioned above. One may either dig a holev into the ground and obtain from the hole a sample of soil air, or he may remove under suitable conditions asample of the subsoil and treat it so that the hydrocarbons are desorbed and can be gathered for analysis.= The former system is the older and apparently simplertechnique but investigators learly determined that there were many inherent disadvantages such as the length of time involved in preparing the'hole and gathering the sample, the contamination from the atmosphere, andthe low permeability of the .soils in some areas making it extremely In collecting subsurface samples byy this method a suitable amount of soil is collected from a point, usually several feet or more below the surface of the earth and is removed inv a sealed container to the laboratory. Here the customary procedure has been to draw olf the sorbed hydrocarbonsbyheating the sample. The sorbed'hydrocarbons are presumably held in a very thin.'l

approximately monomolecular layer on the soil particles with such force that it is necessary, utilizing this prior art technique, to heat the samples to a rather high temperature of the order of 'several lhundred degrees centigrade in order 40 that the hydrocarbons maybe disengaged or desorbed from the soil samples so that they may be collected. I have discovered that there are extremelyserious consequences which can result from this degree of heating of the samples. One `outstanding diiliculty lies in the fact that there are present in the soil not only various minerals and the sorbed hydrocarbons, but also other substances which' I believe to be largely vegetable in nature,

'50 which decompose when heated, 4giving of! in the troleum but is also a product of decomposition of vegetable matter and hence is found in conprocess large volumes of. gases which for convenience I will refer to Vas pseudo-hydrocarbons* .tionwillxbe ncatin. y

- In one` of its broad aspects my invention con templates desorbing rsoil samples and recovering sult. A second andl even more undesirable eilect -oi the strong heating liesin thei'act that any higher-hydrocarbons which have been sorbed in the sample such as eicosane, pentacosane, triacontane, and the like, have a tendency to decompose at these temperatures and to break up or crack into lighter hydrocarbons.V Obviously,

in so doing they will produce a greater volume carbons having upto about eight carbon atoms per molecule, it is possible in accordance with my invention to recover those` containing from ten up to thirty or more carbon atoms per mole-l cule as well as lighter hydrocarbons'.

It 'is anobject oi my invention to provide a method and apparatus for desorbing soil samples of their sorbed hydrocarbon content without excessive heating and thermal decomposition produced thereby. It is a further object of my invention to providea method andapparatus for desorbing soil samples to recover therefrom heavy sorbed hydrocarbons, such as those containing from ten to thirty carbon atoms, and other heavy molecules without decomposing the same. c It is a :further object of this invention to prol vide -a `microanalytical method and apparatus ior the gathering and selective analysis o! sorbed hydrocarbons from soil samples.`

Further object and advantages of my invenunderstood upon reading this speci- Y and other components under conditionsgivinga long mean free molecular path, or, f 1n other words, in a` molecular still.

' .They-accompanying drawings illustrate certain embodiments of my invention. These i'orm'al part of this specication and are to' be read in con- Junction therewith. In these drawings, the same numeral indicates the same or correspondingl Darts' in' all figures.

l of these lighter hydrocarbons which will be meas- Receiverl I6 may be iilled with a liquid from the top. i

Tube I4 is connected through an oil-on stop cock II to lines Iand I9. Line I9 is connected through an olf-on stop cock 20 with line 2l which in turn through oli-on stop cock 22 and line 23 connects with a source of hydrocarbon-free nitrogen 24. Line I8 passes into a trap 25 which can be refrigerated, then into a second trap 26, which also can be refrigerated. An oil-on stop cock 21 connects trap 26 to a line 28 which communicates directly with a mechanical vacuum pump 29, such y as a Hyvac pump, capable of producing a 'vacuum of the order of 1 micron of mercury.

Line -30 communicatesV with line Il. It is connected through ofi-on stop cock 3l to line 32 and rubber tubing 33 which in turn connects with line 34 which passes through a two hole rubber stop' per into the top of iiask 35. ,Another tube 36 extends through the stopper nearly to the bottom oi the nasi; 35. It is connected through a rubber tube to an overflow so that `the contents of this line may be emptied into a graduate 31. A pinch clamp 38 is used in commotion with rubber tubing sa to seal oir one opening to the flask. A pinch clamp 39 is similarly used to seal oif the second opening into flask 35.

Tube I3 is connected by means of otr-on stop cock 40 with lines 4l and 42. Line 42 is c0n' nected through oli-on stop cock 43 and line 44 Y with stop cock 22 and the nitrogen container 24.

VLine 4I is bent to form a trap 45 which may be refrigerated. This isconnected to lines 45 and Line 41 communicates through an oir-on stop cock 48 and line 49, rubber tube and pinch clamp.

assembly 50 and line 4| with a flask 52,' this whole assembly being identical with that from 'Figure 1 is Va, diagrammatic elevatiompartly in -section,' ot one type of apparatusfor desorbing soilfsamples-.of their sorbed.. hydrocarbon content without` decomposition, Y in accordance my invention.

Figures 2, 3 and 4 are diagrammatic 'elevations -ofa portion of the apparatus of Figure 1 together with other lequipment useful in the transfer-of desorbed soil hydrocarbons from the apparatus showntlih'A-.Figure 1 to an analytical-apparatus.

.Figure 5 is a detailed cross-section taken along the line 5-5 of Figure.

v In Figur-er1 a sample of'soil I I is placed in the bottom part of a-iiask I2. This dask is furnished witl itv'r .o ;tubes l.3and I4 and at the toptermi- Ainlstandard groundvjoint I5. A` correspnding ground joint ou receiver Il makes a- .tight connection-with Joint I5. fso that with l `Vt liej.-.ls`e,cita-.very small amount oi high vacuum itis 'possible to make an air tightseal `.i'itthis point. Receiver Il is hollow'andelon'- gated, the lower portion of it extending within a ntimelers ci the soil sampleln flask I2.

'are properly constructed. v

Stop cocks 20, 22, 3l, 4l, 43, and 4l are closed `line 30 to flask 35. Line 53, similar to line 36,

leads through a rubber tube and pinch clamp assembly 54 so that the end of this line can empty into a graduate 55. Graduates 55 and 31 are'approximately ofthe same volumetric capacity as their corresponding flasks 52 and 35.

Line 48 communicates through oil-0n' stop cock 56 and line 51 with a high vacuum pump 55 such as a Langmuir pump. This'in 4turn is con-- nected through line 5! with the mechanical vacuum pump 29.

'I'he operationy of the. apparatus to desorb the soil o i its hydrocarbons and other volatile components is as follows:

Receiver I6 is. removed from ifia-.slr I2. A

weighed quantity of soil sample is placed in ilask I 2. Stop cocine I1 and 4l are closed. The upper part of ground joint I5 is lubricated with a verylow vapor pressure vacuum stop cock grease, such as Apiezon N grease, and receiver II nis `replaced in ask I2, sealing Joint I5. It is, o!

course,V possible to use a mercury seal between the receiver I6 and ask I 2 if it is discovered that vapor from the grease is contaminating the sample but this should never be the case if the joints at the start of the run. Trap 25 is surroimded with a bath oi' subliming carbon dioxide' in a suitable container-and similarly trap 2B is surround ed by a bath of iiquid air. stop cock l1 is opened and pump 29 is started up. This will evacuate A ask I2 .and the hues from this flask to the pump to an ultimate pressure of less than a millimeter of mercury.- Most of the soil air originally in the sample, nearly all oi' the water present,.

and a very small amount cf the adsorbed soil hy- I Agraduate 51.

lclosed.

llr drocarbons are removed from the sample by this procedure. The water vapor and other materials condensable at 78 C. will be condensed in trap 25 while gases which are eondensable between' 78 C. and 'about 188 C. will be condensed in trap25. Oxyen, nitrogen,' methane, and other substances which are non-condensable at. ap" proximately 188 C. `in the respective propor- `tions'present will be pumpedoif from the sys- 1 a stumble apparatus isd'lsciea in United states i' Patent 2,212,681 issued in the name of T. H. Dunn.

During this time the soil sample has been subjected to a very high vacuum ata moderate tem- 5 perature, with a surface at liquid air temperature only a short distance away.n Nearly all the molecules present in the' space above the soill in ask I2 will therefore be removed. Those which are condensable at liquid air temperature will con-l tem. During the latter part of this evacuation, dense either on the surface of receiver I5V or if flask I2 -is surrounded with a bath which I2aA which can be of any suitable liquid such as water or oil, and this is heated to the order of i0 to 50 C. 'Ihe soil II in ask I2 has bynow been swept fairly clean of the materials that are not desired in making the test, i. e. the gases which are not sorbed on thesoil sample, water, etc. On

the other hand, the sample has not been heated suiciently to cause an appreciable amount of thermal decomposition. v After this evacuation. After this evacuation which should take of the order of- 5 to 30 minutes at around 40 to 50 C.; y stop cock I'I is closed off and stop cock L4I) .is opened. Trap 55 is surrounded with a liquid air bath and liquid air is poured into receiverIB.

. The temperature of the bath surrounding flask.

I2 isincreased, and the high-vacuum pump 58is` placed in operation-to evacuate ask I2 and the attendantv system to a nal vacuumv of the order of 0.5 micron of mercury or lower; preferably from about 0.1 to about 0.01 micron. The maxi' mum pressure is such that the mean free path of the. molecules to-bey recovered is about as great or greater than the distance from the upper sur.- faceof the soil sample to the bottom ofthe refrgerated surface ofreceiver I5.

The temperature to which the bath surrounding flask I2 is raised is suiliciently low so that no appreciable decomposition of .soil constituents ocv curs. For the average soil a temperature of the 40 desorption is by now practically complete.^f-Thev Y order of 100 C. is appropriate. Other tempera-l `tures -such as 75 C. to 150 C. can be used.

While this evacuation is taking place, the gases which have condensed in traps 25 and 25 can. be

removed and analyzed for the hydrocarbons pres- 45 ent. Flask 551s removed; lled with water and' replaced. and the pinch clamps 38 and 35 are* Opened- Stop cock 21 is` now closed and the re'-l fngerms :mmtraps :s and ze are removed perthe material has an appreciable vapor pressure at sorbed onthe soil sample at the temperature of around 100 C., combined with the long mean free path of the molecules in the space over `the soil,

be suflicient lunder this condition todrive these hydrocarbons oil from the soil sample so that they will be collected mainly on the refrigerated receiver I5. Since the temperature of the bath surrounding ask I2 is too low to cause appreciable thermal decomposition of the vege` table matter present, there 'will be only a neglif gible amount of pseudo-hydrocarbons formed and thereafter. condensed on the outside of receiver- I5. On the other hand.'A the molecules 'of the heavier hydrocarbons present will not be cracked at the temperature involved and will condense on 'the refrigerated surface of receiver I5 in their true quantities. Finally, it should be noted-that there is no opportunity for contamination of the material condensed on receiver I5 from the mate- -rial'usediin pump 58 (preferably mercury) since any molecules of -this substance will be condensed out on the surface of trap 45. After the ask -I2 has been subjected to the highest vacuum possible for some time, 1preferably of the' order of 20 to 100 lminutes, stop cocks 40 and 55 are closed. The

material condensed-in--trapj5 can .now be analyzed for the presence of hydreabons'by collecting this material in ask 52. Tl@ same procedure is used as was already employexfor collecting/Q then reconnected to line 5I.l Pinch clamps 50- mitting these trapstowarm to room temperature, and 54 are opened. v Nitrogenfrom container 24 'Hydrocarbon-free nitrogen from thesupply under.

' mit nitrogen slowly to flow-through thesystem, displacing the water in flask 35 which flows out 55 are then closed, as are pinch clamps 50 and 54 and the flask 52 containing nitrogen and the volatile y through line into graduate 51. This nitrogen ured bythe amount of water displaced -into the Stop cocks 25 and 22-are\.then

I have found that. oneliter of is a conven( ient amount but other volumes can be used if de- 65 sired. By this'system all' of the condensables from traps 2 5 and 25 are collected in the flask 55.

Pinchv'clamps '55 and 35 are nowclosed and the rubber tube is disconnected from line 52. The ask containing the nitrogen and condensables can nowbe removed and the contentsdisplaced into a suitable micro Vgas analysis apparatus for measurements ofthe hydrocarbons. The type of sas analysisapparatus used for this purpose doe's not form part of my invention. One example of is lswept through the trap by'opening stop cocks ,22, 45 and 45 so that nitrogen slowly flows through constituents from trap 45 can be removed from line 5I and connected .to the micro gas analysis apparatus for measurement. i

'The main body of the hydrocarbonstdesorbed from a soil sample have been condensed on the outer surface of receiver I5 and have not been analyzed'as yet. -There are numerous methods available for removing receiver I5 from this apparatus and `connecting it to a. micro gas analysis apparatus for analysis of the constituents. Thus receiver I5 can be'removed and inserted into any type of analytical apparatus,

One system for removing receiver I5 and analyzing the hydrocarbons .fcondensed thereon will now be described. Nitrogen from container 24 is slowly admitted into flask I2 by opening stop" .cocks 22, 45, and 45 until-the pressure'in nask I2 is approximately atmospheric. The ground joint I5 istlien loosened by turning receiver I5 and it A is then removed from the apparatus. This removal is accomplished by the apparatus shown in Figures 2, 3, and 4. Essentially this consists of a container by means of which the refrigerated' can be pulled up through this opening. The top vent, for lnstance ml., yis slowly poured into thistle tube l2, by means of which the material on the surface of receiver I6 is rinsed into nasi:

59. Receiver i6 can be rotated during this operation, if desired, to increase the effectiveness of the rinse. The flask 69 containing the dissolved material from receiver I6 is now removed from vessel 6l.- The solvent in which the soil hydrocarbons are dissolved is now analyzed for the presence of these hydrocarbons. One excellent method of accomplishing this result has been desc rlbed in United States Patent 2,213,905 issued of the receiver is closed. 'Ihrough this top there I prctrudes a. rod Si iitting loosely in a bearing i2. This rod Si is fitted with tongs 63 which can be lowered over the end of the'receiver i6 to clamp over the constriction near the top of the receiver. A small tube S4 leads into the upper part of the container 60 and is attached through a exible line 65 to a source of hydrocarbon-free nitrogen at a pressure above atmospheric. At the bottom ofthe container there is adisc 66 pivoted near the opening in the bottom of container 60 so that this disc can be rotated to shut olf the bottom of the container.

When the container 5B has been placed over receiver i6 the tongs 63 are engaged and a slow stream of nitrogen is passed in through tube, filling the container with an atmosphere of nitrogen. The receiverl is then rapidly pulled up into the container by means of the knob at the upper end of the rod 6i and the disc 66 is swung into place shutting off the bottom of the. container. The atmosphere inside the container is at a pressure slightly greater than atmospheric so that nitrogen leaks from the container and no air, which might contain stray hydrocarbon vaporsI can contaminate the hydrocarbons condensed on thewallofethe receiver i6. The container in"clsed position is shown in Figure 3.

The receiverv i6 is removed in' this container to anrapparatus in which the hydrocarbons can be withdrawn from the cold surface of the receiver without contamination. One such apparatos is shown in Figure 4. The chief member of the apparatus is a vessel El, the top of which is formed with a ground joint eiactly similar to joint i5. The lower part of this vessel is constricted into a tube 68. Before removing condensed substances from receiver I6, a. flask 69 is connected to tube 68 by means'of a nonlubricated ground joint 10. Near the upper end of vessel 61 there is a. side tube 1 l which communicates with a funnel or thistle tube 12. Side tube 'li is bent to form trap 13 and terminates in a nozzle 14 which'can suitably the directed tangentially to the cylindrical surface of receiver i8 as shown in Figure 5. Y

A hydrocarbon solvent. the refractive index of ,which has` been very carefully measured with a precision refractometer. is poured into thistle nube 12 until there is sumcient liquid in trap I3 to seal tube ll. Receiver IG yis placed over this apparatus, preferablyV preilushed with hydrocarbon-free nitrogen, disc 66 is swung out of the way and rod 6I' is lowered until the ground joint on receiver IB is seated in the ground joint of vessel 61. The hydrocarbons on the surface of receiver i6 are now no longer in dangerrof contamination from hydrocarbons in the air, s o the nitrogen-supply is cut olf from line l5, the tongs 63 are opened, and container il is removed. The liquid air in receiver I6 is now re` in the` name of -Joseph B. Clark. It is shown in that patent that the refractive index of the solvent varies with the amount and type of soil hydrocarbons dissolved in it and hence by suitable measurement of the refractive index of the solvent before and afterv dissolving the hydrocarbons in it, one can obtain a. measurement of the quantity' of hydrocarbons present. Alternatively a, diiferential refractometer can be employed to measure the change in refractive index of the hydrocarbon solvent occasioned'by the rinsing operation.

Suitable solvents for use in this type of measurement include carbon disulde, benzene, cyclohexane. pentane, etc. I prefer to use, in general, solvents having a higher refractive index than that of the hydrocarbons present, such as carbon disulfide, but solvents of lower refractive index can be used. In order to avoid errors in the analysis due to the presence of water on the surface of receiver I6, which has been removed from the soil sample, I prefer to saturate the hydrocarbon solvent with water before commencing operations. The refractive index of the water saturated solvent is measured, the solvent is then used to rinse the surface of receiver IS and another measurement of the refractive in dex is then made. use anhydrous solvent and pass the material collected in flask 69 through a dehydratlng agent -before the nal measurement as an alternative means of eliminating the effect of water collected with the other material condensed on receiv- -'er I6. l

This method of v condensed on the walls -of receive I6 is but on'eof several alternative methods. Other methods will suggest themselves to those skilled in the art. LNeither is it imperative to use the refractive index method of analysis for the condensed ma.

terial, since other known methods of analysis can be used.

Another method of analysis'which is to-be preferred where very accurate separation of the various hydrocarbons removed from the soil by the above desorbing method is desired, is to a1- low the hydrocarbons from receiver i6 whichhave been freed from 'the surface by warming itI to pass into a mass spectrograph. It is well known that very small amounts of various substances` l can be determined by use of such an instrument. Y

- May 1940, page 13.

moved and the receiver permitted to warm. A

standardizedquantity of the hydrocarbon sol- While I have described my invention in connection with a 'preferred'embodiment thereof, it will'be understood that this is byway of illustration and not by way of-limitation and that I do not mean to be restricted theretobut only n tothe scope of the appended claims.V In per- 0f course. it is possibletol removing the hydrocarbons I prisingY a molecular still 'for desorhing -said sample reservoir being connectedwith said trap,means for passing a hydrocarbon-free gas through said 'trap and into said reservoir to transfer hydrocarbons from said trap to said reservoir, an additional trap alternatively connected with said molecular still, means connected with said additional trap and with said molecular still forA further evacuating said.' molecular still'and similarly evacuating said additional trap. a second sample reservoir `for heavy hydrocarbons, and meansconnected with said additional-trap and with said second sample reservoir iorpassing a hydrocarbon-free gas through said additional trap and into said second sample reservoir.

2. Apparatus for geochemical surveying combons from a soil sample, at leastone trap connected tosaid molecular still for trapping hydrocarbons desorbed from said soil sample, means liydrocarA s,s14 ,iss

desorbed from said-soil sample, means connectedwith said molecular ,still and with said trap for evacuating said molecular still and said trap, a sample reservoir for .light hydrocarbons, said sample reservoir being connected with said trap and means for passing a hydrocarbon-free gas through said trap and into said reservoir to transfer said light hydrocarbons from said trap to said reservoir.

i. Apparatus for geochemical surveying comprising a molecular still for desorbing hydrocar- -bons from said soil sample, said molecular still including means having a refrigerated surface vfor collecting hydrocarbons desorbed from said soil sample, said means being removable from said still, at least one trap connectedto said molecular still for trapping hydrocarbons desorbed from said soil sample which are not collected on said refrigerated surface, means connected with said molecular still and with' said trap for evacuatlin'g said molecular still and said trap, a sample reservoir for hydrocarbons, lsaid sample reservoir'being connected with said trap, and means for passing ahydrocarbon-free gas through said trap and into said reservoir to transfer said hydrocarbons from said trap to said reservoir.

connected with said molecular still and with said trap for evacuaiing said molecular still and said trap, a sample reservoir for light hydrocarbons, said sample reservoir being connected with said trap, and' means for passing a hydrocarbon-tree -gasthroughsaid trapandintosaid reservoirto transfer hydrocarbons from said trap to said 3.. '1or geochemical surveying compricing a molecular still for desorbing hydrocarbonsiromasoilsamphsaidmolecularstlllincluding means having a refrigerated surface tor 0. soil a sample reservoir for light hydro.

collectingheavyhydrocarbons delmbeiiiroxnsaid soilgmplefat least one trap connected to said moioeularstin for trapmng light lmlrocarbons 5. Apparatus for geochemical surveying com-A prising a molecular still for desorbing hydroi'rom a soil sample, said molecular still including means having a refrigerated surface for collecting heavy hydrocarbons desorbed from said soil sample, said means beingremovable from said still, at least one trap .connected to said molecular still for trapping light hydrocarbons Adesorbed from said soil sample, means connected with said molecular still and with said trap torV evscuating said trap and said molecular still to a pressure suchthat the mean free path oi the beingdesorbedisatleastassl'eatas the said refrigerated surface to the carhons, said` sample reservoir-'being connected with said trapland means for' ahydrocarbon-tresses through said trap and into said reservoir to transfer said light Vhydrocarbons from said trap to said reservoir.

' EDWIN E. ROPER. 

